Dynamoelectric machine balanced rotor



April 22, 1952 H M NORMAN 2,594,203

DYNAMOELECTRIC MACHINE BALANCED ROTOR April 22, 1952 H. M. NORMAN 2,594,203

DYNAMOELECTRIC MACHINE BALANCED ROTOR Filed Jan. 29, 1948 2 SHEETS-SHEET 2 sTAxzToF wmome FENUOF WND'NG Patented Apr. 22, 1952 DYNAMOELECTRIC MACHINE BALANCED ROTOR Horace M. Norman, Skokie, Ill., assgnor to Stewart-WarnerCorporation, Chicago, Ill., a corporation c! Virginia ApplicationJanuary 29, 1948, Serial No. 5,062

3 Claims.v 1

The present invention relates to rotors for electric motors, and more Aparticularly'toan improved core lamination and a method of assembling the laminations to form a rotor having improved static and, preferably, also dynamic balance. The presentapplication is a continuation-in-part of my copending application Serial No. 700,701, i-lled October 2, 1946, now abandoned.

Lack of mechanical balance which is a common defect in rotors as presently constructed maybe due to one or more of several causes and has resulted in the past. in the resort to various expedients to secure the proper balance, such as the addition or subtraction of material atcertain points on complete rotors `to balance them.

Two of the primary causes for anl unbalanced condition in a rotor are the lack of symmetry in the core windings and the fact that thel stock from which the laminations of the core aremade is often tapered across the'grain so that one edge of the stock is thinner and lighter in weight than the other edge. A core made from laminations punched from tapered stock and stacked on the rotor shaft all in the same direction that they were punched is bound to be unbalanced.

According to the presentinvention, the effect of both of these factors can be offset by constructing a core from vlaminations slightly heavier at the region thereof where the core winding is lighter, so that the reduced weight of the winding at thisregion` isbalancediby the added weight of the laminations at that region of the core, and by stacking the. laminations with the grain running in alternate directions, in a manner to be described ingreater` detail hereinafter.

A primary object oi the invention isthe provision of a new and improved laminatedrotor for electric motors in which the core laminations at the region where the rotor coil windings are lighter are of increasedv weight relativefto the weight of corresponding portions of the rest of the core lamination to compensate for the reduced weightof the rotor coils at this region in the assembled core and in .which the ycore laminations are stacked together in suche manner that differences in weight along the pe riphery thereof due to unevenness in the stock from which they are cut is minimized.

Another object of the invention is the. provision of a new and improved laminatedrotor construction for electric motors' having corelamina tions formed so thatra slight increase in weight of the core is secured at the region-.thereof where the core winding is the lightestwhichregion may be where or near where the core winding is started.

A further object of the invention is the provision of a new and improved-method` of stack;- ing core laminations which: minimizes 'and can be used to eliminate substantially completely the` unbalanced condition which might result from the fact that the core laminations are formed from lstock which may taper from one side to the other. The method can be used. for the sake of standardization. on all stock, i. e., both tapered and untapered, so that, should the stock be tapered, the unbalance will be minimized or eliminated.

A still :further object of the invention is the provision of a new and improved rotor for electric motors having an improved static and dynamic balance. y

These and other objects lof the invention will become apparent from the ensuing description in the course of which reference will be had to the accompanying drawings, in which:

Fig. l is a plan view of a single core lamination for the rotor of an electric motor;

Fig. 2 is a plan view of one of the end insulator laminations for a rotor core;

Fig. 3 is a side elevational view of the core laminations and end insulators assembled upon a rotor shaft ready to receive the winding;

Fig. 4 is a side elevational view of a completed rotor constructed in accordance with the invention;

Fig. 5 is an end elevational view ofv an assembled rotor taken from the commutator end of the rotor; and

Fig. 6 is a diagrammatic view showing the manner in which the rotor coils of the rotor are wound upon the rotor core.

The congurations of a rotor core lamination I2 and a rotor core end insulating lamination I4 from which a rotor core is built up are shown in Figs. 1 and 2, respectively. It will be noted that the illustrated core lamination I2 is circular in shape and with a series of equally spaced radially extending arms or teeth I6 which define a series of slots I8 between the adjacent edges of adjoining teeth. A central aperture 20 is also provided which should be accurately concentric with the periphery of the lamination.

The end insulators I4 are provided with a number of teeth 22 equal to the number of teeth on the core lamination I2, and these teeth dene a series of slots 24 between the adjacent edges thereof. The end insulators are also provided with a central aperture 26 concentric with the periphery of the insulator.

In the illustrated embodiment of theinvention, the slots I8 in the juxtaposed core laminations I2 of an assembled rotor and the slots 24 in the end insulators I4 receive the windings which form the rotor coils of the finished rotor so that the number of teeth and hence the number of slots inthe laminations will be determined by the number of rotor `coils with which the rotor is to be equipped and need not be limited to eleven as @o shown -in the drawings.

All of the teeth I8 on the core laminations are of uniform shape so that they will be of uniform weight except the teeth which have been marked Ia and |611. Portions of the adjacent edges of these two teeth are bulged outwardly slightly as compared with the corresponding edges of the other teeth on the laminations, as indicated at" 23, so that the weight of the core in the region of these two teeth is increased slightly-relative to the weight of the other teeth for a purpose which will be explained presently.

In an assembled core 30, as shown in Fig. 3, a plurality of core laminations I2 are secured in juxtaposed relation upon a rotor shaft 32 with the apertures 2l! engaging over the shaft 32 and an end insulator I4 located at each end of the stack of core laminations. The core laminations are secured on the rotor shaft 32 in a conventional manner, such as by press fitting the same upon a knurled portion of the shaft. Sleeves 34 are secured to the shaft in abutting relation with laminations to make a convenient shoulder for locating the commutator at one end and a support for washers which take the end thrust at the other end. I

When a plurality of core laminations I2 are being stacked to form an assembled core, the slots I8 formed between the adjacent teeth I6a and Ib of the different laminations are prefer` ably, but not necessarily, arranged in aligned relation along a line which is skewed approximately degrees from the normal so that a skewed transverse slot cell 36 adjacent the periphery of the core 35 is formed by the juxtaposed laminations I2, as seen in Fig. 3. Since all the other teeth I6 are uniform in shape and equally spaced from each other, they will also be positioned in aligned relation the same -as the weighted teeth and will define other skewed slot cells 36 through the core. The slot cell formed between the weighted teeth IBa and Ib is preferably identified by marking the surface of the co-re along this slot cell with a layout fluid or other colored fluid, and this may be done as the laminations are stacked off the punched press on which they are formed.

As a result of the slightly increased weight ol' the core teethy a and ISb and the manner oil stacking the laminations, the assembled unwound core isslightly heavier on one side than on the other. This added weightv on teeth I6a and Ib is designed so that it is sufficient to offset the unbalance which has been found to be present in conventionally constructed rotors due to the lack of symmetry in the rotor coil windings, which unbalance generally has its resultant at or near the slot -cell where the coil windings start and end. Should the winding be lightest at a, region other than the slot, the added weight may be placed at that region. For example, the winding may be lightest at the region of a tooth. In this case, that tooth may be enlarged somewhat at both sides. In some cases, the region at which the winding is lightest may be displaced one slota-way from where the winding begins and ends. In this case the winding can be started at the next slot sothat'the lightest region of the winding substantially coincides with the region of the core whereat weight is added.

The rotor rmay be wound in conventional manner and connected to segments 38 on a commutator 4G secured on one end of the rotor shaft 32 against the sleeve 34 and insulated fromA the shaft 32. f

An insulating cap 42 'is placedover the winding 4 between the commutator and the end of the core to insulate the ends of the rotor coils, thereby better to insulate the leads that are soldered to the commutator.

The rotor core 3G shown in the drawings is 4provided with eleven rotor coils; hence, eleven Ysegments 38 are provided on the commutator i connected to separate binding posts 46 projectingv from' the commutatore exteriorly of the cap 42. A separate lead 48 connects each binding post 46 Yto the junctions of the rotor coils.

One manner of winding the rotor coil windings is illustrated diagrammatically in Fig. 6 in which the slots between the teeth have been numbered from one Ato eleven to simplify the explanation, the weighted teeth being indicated at Ia and IBb, as before. The commutator segment to which the starting end of the winding is connected is indicated at 38a and the winding for the rst coil which is shown diagrammatically in full lines starts at the commutator side of the core and extends between and is laid in slots I and 6. Although only two turns have been shown, it will be understood that a rotor coil consists of a relatively large number of turns. However, only two are shown in order to eliminate confusion. The beginning of the second coil is shown in dotted lines and the winding forming this coil extends between and is laid in slots 2 and l. The rest of the eleven coils are wound in a similar manner, and the eleventh and last coil, which is shown in dash lines, extends between and lies inthe eleventh and fifth slots.

It has been found that by winding the coils in thismanner with both the starting and the terminal ends of the winding in the slot cell 36 formed between therweighted teeth ISa and Ib, the winding is generally lighter in the region between these teeth. Thus, by making these teeth heavier, the resulting unbalance can be elimihated; However, as pointed out earlier, should the winding be lighter elsewhere than between vthe teeth, weight can be added elsewhere to achievethe desired compensation.

Another factor affecting the balance of a rotor arises: as a result of certain peculiarities which may bel present in the relatively thin sheet steel stock from which the core laminations I2 are formed. It has been found that such stock often has a slight taper across the grain of the stock so that it is thickeron one side than the other and, as 'a' result, heavier on the thicker side. A series of the laminations punched in the same direction from this stock will of course each be heavier'along one portion thereof and hence will be slightly unbalanced. If these laminations are all stacked in the same direction in which they were punched from the stock, the assembled core formed thereby will be unbalanced.

' VInaccor'dance with one of the features of the present invention, the core laminations I2 for a rotor core are all punched in the same direction from the stockV and then so arranged and secured as to minimize the unbalance resulting from any taper 'whichmay be present. Substantially complete elimination, if desired, and it usually is, canbe attained by having substantially equal numbersA of laminations with the taper extending in opposite directions. One way of doing this is to stack one group of adjacent laminations with the taper extending in one direction and another group of adjacent laminations with the taper extending in a direction degrees removed from the direction ofthe taper in the first group. This 

